1. Field of the Invention
The present invention relates to a barge for use in the bulk transport of materials.
2. Description of the Related Art
One important use of marine barges is in the bulk transfer of materials used in land reclamation projects. Such projects require the transport of large volumes of aggregates (sand and the like) that are dredged at one location (e.g. from the seabed), loaded onto the barges and discharged at a site where land is being reclaimed. To date land reclamation projects have employed hopper barges and dump barges to move aggregates to a desired site.
Hopper barges comprise a large hulled vessel containing a number of hatch compartments with hopper gates mounted at the bottom of the hatch compartment. In use Hopper barges are anchored at a supply site, where material is loaded into the hatches of the hopper barge or drawn from the sea-bed or river bed and pumped (e.g. using a suction dredger) in semi-liquid form into the hatches of the hopper barge. Once the hatches are full the Hopper barge moves to the reclamation site to unload its cargo. Discharging is carried out by opening hopper gates located in the bottom of the hatches below the water line. It is crucial to ensure that the barge operates in water of sufficient depth. If the water is too shallow the barge may become grounded on the material released through the hoppers. Once the material has been discharged the hopper barge travels back to the supply site and the cycle repeats.
Hopper barges are able to quickly unload materials at the target site. However, it requires deep water for its hopper gate maneuver. Such barges therefore have the disadvantage that they are not able to operate in shallow waters.
The inability of hopper barges to operate in shallow waters is attributed to a number of factors including:
(1) The hatch compartment is located within the center core of the vessel, sandwiched and surrounded by its hull. This means the vessel must be designed such that the holding compartment only comprises about one third of the vessels volume in order that reasonable buoyancy and stability standards may be maintained. This required volume is a disadvantage in itself but also has the effect that the barge cannot operate in shallow waters.                (2) The hopper barge must be in water that is sufficiently deep enough to allow the hopper gates to swing open. It is particularly important that there is sufficient room for the gates to close when the cargo has been discharged.        
A further disadvantage associated with hopper barges is that they are prone to mechanical failure. The mechanical system that operates the hopper gate often breaks down due to exposure to sea water as well as contact, wear and tear with gravel material. Accordingly hopper barges also suffer from high maintenance costs and the capital cost of a hopper barge is high, relative to a dump barge (see below) capable of transporting an equivalent cargo volume.
Dump Barges are large vessels with large capacity open decks that may be loaded with a cargo. In use the dump barge is anchored at a supply site where material is loaded onto the open deck of the dump barge or drawn from the sea-bed or river bed and pumped (e.g. using a suction dredger) in semi-liquid form onto the top open deck of the dump barge. Once the barge is loaded to capacity it is moved to the reclamation site and the cargo discharged. The material is discharged by opening up side fender gates surrounding the loaded deck and then pushing out the material directly from the deck side. Pushing activity may be carried out manually or by mechanical shovel (e.g. a bulldozer). Once unloaded the barge travels back to the supply site and the cycle repeats.
Dump barges have the advantage that they can operate in shallow water or may even be beached before the unloading process begins. The ability of a dump barge to operate in shallow waters is related to the fact that the vessel has a high buoyancy value. This is because its hull is empty right to the bottom (unlike hopper barges) and the vessel is also rectangular in cross-section.
Furthermore, the shape of dump barges offers a high holding capacity (generally superior to hopper barges) because the entire top, open deck is engineered to receive cargo. Loading capacity is determined during the registration of a vessel with an approved authority. Construction, engineering features, technical specifications and age are taken into consideration. Generally speaking dump barges are allocated greater loading capacities than hopper barges.
Despite the above mentioned advantages of dump barges, they have a major draw back in that the unloading process is very slow even with the aid of individual mechanical shovels, bulldozers and the like. This is because movement of mechanical shovels and the like is hampered by the sheer volume of a fully loaded cargo deck. Assigning additional or higher capacity stand-in equipment not only cannot resolve the problem, but also adds cost and also reduces the capacity of its holding area. Under such physical constraints land-fill material can only be pushed in to the sea, shovel by shovel, by a limited allowable number of on-board stand-in equipment. This is cumbersome and time consuming.